Multilayer low reflectivity hard mask and process therefor

ABSTRACT

A method utilizing a multilayer anti-reflective coating layer structure can achieve low reflectivity at high numerical apertures. The multilayer anti-reflective coating structure can be utilized as a hard mask forming various integrated circuit structures. A multilayer anti-reflective coating structure can be utilized to form gate stacks comprised of polysilicon and a dielectric layer. A photoresist is applied above the multilayer anti-reflective coating which can include silicon oxynitride (SiON) and silicon rich nitride (SiRN).

This application is a divisional application of U.S. patent applicationSer. No. 12/468,715, entitled “MULTILAYER LOW REFLECTIVITY HARD MASK ANDPROCESS THEREFOR”, filed May 19, 2009, now U.S. Pat. No. 8,048,797 whichis a divisional application of Ser. No 11/098,262, now U.S. Pat. No.7,538,026, entitled “MULTILAYER LOW REFLECTIVITY HARD MASK AND PROCESSTHEREFOR”, filed Apr. 4, 2005.

FIELD OF THE INVENTION

The present specification relates to the fabrication of integratedcircuits (ICs). More specifically, the present specification relates toa hard mask process for forming integrated circuit features.

BACKGROUND OF THE INVENTION

Semiconductor devices or integrated circuits (ICs) can include millionsof devices, such as, transistors. Ultra-large scale integrated (ULSI)circuits can include complementary metal oxide semiconductor (CMOS)field effect transistors (FET). Despite the ability of conventionalsystems and processes to fabricate millions of devices on an IC, thereis still a need to decrease the size of IC device features, and, thus,increase the number of devices on an IC.

One limitation to the smallness of IC critical dimensions isconventional lithography. In general, projection lithography refers toprocesses for pattern transfer between various media. According toconventional projection lithography, a silicon slice, the wafer, iscoated uniformly with a radiation-sensitive film or coating, thephotoresist. An exposing source of radiation illuminates selected areasof the surface through an intervening master template, the mask, for aparticular pattern. The radiation can be light, such as ultra-violetlight, vacuum ultra-violet (VUV) light and deep ultraviolet light. Theradiation can also be x-ray radiation, e-beam radiation, etc.

The lithographic photoresist coating is generally a radiation-sensitivecoating suitable for receiving a projected image of the subject pattern.Once the image is projected, it is indelibly formed in the coating. Theprojected image may be either a negative or a positive image of thesubject pattern.

Exposure of the lithographic coating through a photomask or reticlecauses the image area to become selectively either more or less soluble(depending on the negative or positive photoresist coating) in aparticular developer. The more soluble areas are removed in thedeveloping process to leave the pattern image in the coating as lesssoluble polymer.

The photoresist material or layer associated with conventionallithographic technologies is often utilized to selectively form variousIC structures, regions, and layers. Generally, the patterned photoresistmaterial can be utilized to define doping regions, implant regions orother structures associated with an integrated circuit (IC). Aconventional lithographic system is often utilized to patternphotoresist material to form gate stacks or structures. As the featuresin semiconductor patterning become smaller and smaller, the photoresistthickness needed to sustain reasonable aspect ratio must decrease. Athinner photoresist may not be suitable for etch applications due topremature resist erosion. Thus, resist erosion complications facilitatethe necessity for hard mask processes.

According to one conventional process, a hard mask is provided abovepolysilicon/oxide layers to pattern the gate stacks. The hard mask mustbe thin enough so that it can be etched without eroding the patternedphotoresist above it. The hard mask must also be thick enough towithstand an etch process so that uncovered portions of the underlyinglayer (e.g., polysilicon layer) can be completely removed. Accordingly,the hard mask must have a precise thickness to appropriately pattern thegate stacks.

An anti-reflective coating (ARC) has been conventionally providedunderneath the photoresist material or the hard mask to reducereflectivity and thereby, reduce resist notching, lifting and variationof critical dimension of the obtained pattern. Generally, the ARC(organic or inorganic) is a relatively thin layer which cannot be usedas a hard mask because it is too thin and does not allow thicknessflexibility due to optical design parameters.

Advanced lithography is utilizing higher numerical apertures (NA) toachieve smaller feature sizes. However, the use of higher NA affects thereflectivity of the ARC. The effects on reflectivity associated withhigher NAs makes designing a optimal thicknesses for an ARC moredifficult. For example, reflectivity requirements due to the use ofhigher NA's and thickness requirements for bottom anti-reflectivecoatings (BARCs) are not coincident.

Thus, there is a need to pattern IC devices using non-conventionallithographic techniques. Further, there is a need for a process offorming a gate stack that does not require a conventional hard maskstep. Yet further, there is a need for a hard mask that has lowreflectivity at high NA. Even further still, there is a need for a gatemask process that effectively balances optical and etching efficiencies,especially at ultra high NA. Yet even further still, there is a need fora dual layer hard mask that has less than 1% reflectivity at high NAsand can be used with dual poly flow processes.

SUMMARY OF THE INVENTION

An exemplary embodiment relates to a method of fabricating an integratedcircuit. The method includes providing a first anti-reflective coatinglayer including SiOC, SiRN or SiON above a substrate; providing a secondanti-reflective coating layer including SiON or SiOC above the firstanti-reflective coating; providing a photoresist layer above the secondanti-reflective coating layer; patterning the photoresist layer. A firstthickness of the first anti-reflective coating and a second thickness ofthe second anti-reflective coating are configured to reduce reflectionsassociated with the patterning step to below 0.2 percent. The methodfurther includes removing the first anti-reflective coating layer andthe second anti-reflective coating layer in accordance with a featuredefined by the photoresist layer.

Another exemplary embodiment relates to a method of forming a gate stackfor an integrated circuit. The method includes providing a firstanti-reflective coating layer and a second anti-reflective coating layerover a gate conductor layer. The second anti-reflective coating layerincludes silicon, oxygen and nitrogen. The first anti-reflective coatinglayer includes silicon and nitrogen. The method also includes steps ofproviding a photoresist layer over the second anti-reflective coatinglayer, and patterning the photoresist layer to form a first feature inthe photoresist layer at a high numerical aperture.

Still another exemplary embodiment relates to a method of forming a hardmask for an integrated circuit. The method includes steps of providing adual layer anti-reflective coating above a substrate, the coatingincluding at least silicon oxynitride and silicon rich nitride. Themethod also includes steps of providing a photoresist layer above thedual layer anti-reflective coating, patterning the photoresist layer toform a feature, and selectively removing the dual layer anti-reflectivecoating in accordance with the photoresist feature.

Another exemplary embodiment relates to a method of forming a hard maskfor an integrated circuit. The method includes providing a dual layeranti-reflective coating above a substrate, providing a photoresist layerabove the dual layer anti-reflective coating, and patterning thephotoresist layer to form a feature. The method also includesselectively removing the dual layer anti-reflective coating inaccordance with the photoresist feature. The coating includes at leastone spin-on organic anti-reflective material and at least one of asilicon nitride (Si₃N₄), carbon doped silicon oxide (SiOC), siliconoxynitride (SiON), and silicon rich nitride (SiRN) layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The exemplary embodiments will hereafter be described with reference tothe accompanying drawings, wherein like numerals denote like elements,and:

FIG. 1 is a general schematic block diagram of a lithographic system forprocessing a substrate according to an exemplary embodiment;

FIG. 2 is a schematic cross-sectional view of the substrate illustratedin FIG. 1, showing a first anti-reflective coating deposition step inaccordance with an exemplary embodiment;

FIG. 3 is a schematic cross-sectional view of the substrate illustratedin FIG. 2, showing a second anti-reflective coating layer depositionstep in accordance with an exemplary embodiment;

FIG. 4 is a schematic cross-sectional view of the substrate illustratedin FIG. 3, showing a photoresist layer application step in accordancewith an exemplary embodiment;

FIG. 5 is a schematic cross-sectional view of the substrate illustratedin FIG. 4, showing a photoresist patterning step in accordance with anexemplary embodiment;

FIG. 6 is a schematic cross-sectional view of the substrate illustratedin FIG. 5, showing a trim etching step in accordance with an exemplaryembodiment;

FIG. 7 is a schematic cross-sectional view of the substrate illustratedin FIG. 6, showing a first anti-reflective coating layer etching step inaccordance with an exemplary embodiment;

FIG. 8 is a schematic cross-sectional view of the substrate illustratedin FIG. 7, showing a second anti-reflective coating layer etching stepin accordance with an exemplary embodiment;

FIG. 9 is a schematic cross-sectional view of the substrate illustratedin FIG. 8, showing a gate stack etching step in accordance with anexemplary embodiment;

FIG. 10 is flow diagram showing a multilayer anti-reflective coatinglayer process of etching a substrate or a layer above a substrate;

FIG. 11 is a graph showing reflectivity across a spectrum ofcoefficients of extinction (k) for the bottom and top anti-reflectivecoating layers;

FIG. 12 is a graph showing reflectivity at different numerical aperturesand across the spectrum of coefficients of extinction (k) for the topanti-reflective coating;

FIG. 13 is a graph showing substrate reflectivity versus numericalaperture where the bottom anti-reflective coating layer has acoefficient of extinction of k=0.35 and the top anti-reflective coatinglayer has a coefficient of extinction of 0.25;

FIG. 14 is a graph showing substrate reflectivity versus numericalaperture where the bottom anti-reflective coating layer has ancoefficient of extinction of k=0.35 and the top anti-reflective coatinglayer has a coefficient of extinction of 0.35;

FIG. 15 is a graph showing substrate reflectivity versus numericalaperture where the bottom anti-reflective coating layer has acoefficient of extinction of k=0.35 and the top anti-reflective coatinghas a coefficient of extinction of k=0.45;

FIG. 16 is a graph showing substrate reflectivity versus numericalaperture where the bottom anti-reflective coating layer has acoefficient of extinction of k=0.35 and the top anti-reflective coatinghas a coefficient of extinction of k=0.55;

FIG. 17 is a graph showing substrate reflectivity versus numericalaperture where the bottom anti-reflective coating has a coefficient ofextinction of k=0.25 and the top anti-reflective coating has acoefficient of extinction of k=0.35;

FIG. 18 is a graph showing substrate reflectivity versus numericalaperture where the bottom anti-reflective coating has a coefficient ofextinction of k=0.35 and the top anti-reflective coating has acoefficient of extinction of k=0.35;

FIG. 19 is a graph showing substrate reflectivity versus numericalaperture where the bottom anti-reflective coating has a coefficient ofextinction of k=0.45 and the top anti-reflective coating has acoefficient of extinction of k=0.35;

FIG. 20 is a graph showing substrate reflectivity versus numericalaperture where the bottom anti-reflective coating has a coefficient ofextinction of k=0.55 and the top anti-reflective coating has acoefficient of extinction of k=0.35;

FIG. 21 is a graph showing substrate reflectivity versus numericalaperture with a 100 Å oxide layer over a polysilicon structure where thebottom anti-reflective coating is 400 Å thick;

FIG. 22 is a graph showing substrate reflectivity versus numericalaperture with a 200 Å oxide layer over a polysilicon structure where thebottom anti-reflective coating is 300 Å thick;

FIG. 23 is a graph showing reflectivity across a spectrum of refractiveindices for a 350 Å thick bottom anti-reflective coating and thicknessesfor the oxide layer;

FIG. 24 is a graph showing reflectivities across a spectrum of numericalapertures and thicknesses for the oxide layers where the bottomanti-reflective coating is 400 Å thick and the top anti-reflect layer is300 Åthick;

FIG. 25 is a graph showing reflectivities across a spectrum of numericalapertures and thicknesses for the oxide layer where the bottomanti-reflective coating is 300 Å thick;

FIG. 26 is a graph showing substrate reflectivity versus the thicknessof the oxide layer using a low k SiON/high K SiRN structure;

FIG. 27 is a graph showing substrate reflectivity versus the thicknessof the oxide layer using a dual SiON anti-reflective coating structure;

FIG. 28 is a graph showing reflectivity across a spectrum of numericalapertures and thicknesses of the oxide layer for a dual SiONanti-reflective coating structure;

FIG. 29 is a graph showing reflectivity across thicknesses of the topanti-reflective coating and the bottom anti-reflective coating where thetop layer is an SiON layer with k=0.35 and n=1.8;

FIG. 30 is a graph showing reflectivity across a spectrum of thicknessof the top anti-reflective coating and the bottom anti-reflectivecoating where the top layer is an organic BARC layer with k=0.50 andn=1.8;

FIG. 31 is a graph showing reflectivity across a spectrum of thicknessof the top anti-reflective coating and the bottom anti-reflectivecoating where the top layer is SiON (n=1.8, k=0.35) and the bottom layeris above a 1000 Å oxide layer;

FIG. 32 is a graph showing reflectivity across a spectrum of thicknessof the top anti-reflective coating and the bottom anti-reflectivecoating where the bottom layer is above a 1000 Å thick oxide layer andthe top layer is SiON (n=1.8, k=0.5);

FIG. 33 is a graph showing substrate reflectivity versus numericalaperture for a dual BARC spin-on structure above a 1000 Åpolysiliconlayer;

FIG. 34 is a graph showing substrate reflectivity versus numericalaperture for a dual BARC spin-on structure above a 1000 Å SiON layer;

FIG. 35 is a graph showing substrate reflectivity versus numericalaperture for an inorganic dual BARC spin-on structure above a 1000 Åpolysilicon layer;

FIG. 36 is a graph showing substrate reflectivity versus numericalaperture for an inorganic dual BARC structure above a 1000 ÅSiON layer;

FIG. 37 is a graph showing reflectivity versus a spectrum of numericalapertures and thickness for the oxide layer where the bottomanti-reflective coating is 400 Å thick;

FIG. 38 is a graph showing reflectivity versus a spectrum of numericalapertures and thickness of the oxide layer where the bottomanti-reflective coating is 300 Å thick;

FIG. 39 is a graph showing reflectivity across a spectrum thickness ofthe oxide layer and the polysilicon layer;

FIG. 40 is a graph showing reflectivity across a spectrum of thicknessesof the top anti-reflective coating and the bottom anti-reflectivecoating above a 450 Å thick oxide layer;

FIG. 41 is a graph showing substrate reflectivity versus the thicknessof oxide below a 500 Å thick polysilicon layer;

FIG. 42 is a graph showing substrate reflectivity versus the thicknessof the oxide layer above a 500 Å thick polysilicon layer and 600 Åthickoxide layer using a 250 SiON top anti-reflective coating and a 300Åbottom SiRN anti-reflective coating;

FIG. 43 is a graph showing substrate reflectivity versus the thicknessof the oxide layer using a 200 Å SiON top anti-reflective coating and a300 Å SiRN bottom anti-reflective coating;

FIG. 44 is a graph showing substrate reflectivity versus the thicknessof the oxide layer using a 300 Å SiON top anti-reflective coating and a300 Å bottom SiRN bottom anti-reflective coating;

FIG. 45 is a graph showing substrate reflectivity versus the thicknessof the top anti-reflective coating using a 450 Å thick oxide layer abovea 500 Å polysilicon layer above a 600 Å oxide layer;

FIG. 46 is a graph showing reflectivity across a spectrum of thicknessesof the top anti-reflective coating and the bottom anti-reflectivecoating for a spin-on dual BARC structure above a 300 Å SiO₂ HM oxidelayer above a polysilicon layer;

FIG. 47 is a graph showing substrate reflectivity versus the thicknessof the top anti-reflective coating wherein the bottom anti-reflectivecoating is provided above a 200 Å silicon dioxide layer;

FIG. 48 is a graph showing substrate reflectivity versus the thicknessof the first anti-reflective coating wherein the bottom anti-reflectivecoating is provided above a 300 Å silicon dioxide layer; and

FIG. 49 is a graph showing substrate reflectivity versus the thicknessof the top anti-reflective coating wherein the bottom anti-reflectivecoating is provided above a 400 Å silicon dioxide layer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a substrate 12 is shown in a lithographic system10. Substrate 12 can be a semiconductor substrate, such as, silicon,gallium arsenide, germanium, or other substrate material. Substrate 12can include one or more layers of material and/or features, such as,lines, interconnects, vias, doped portions, etc., and can furtherinclude devices, such as, transistors, microactuators, microsensors,capacitors, resistors, diodes, etc. Substrate 12 can be an entire ICwafer or part of an IC wafer. Substrate 12 can be part of an integratedcircuit, such as, a memory, a processing unit, an input/output device,etc.

Lithographic system 10 provides a pattern of radiation to substrate 12.System 10 can include a chamber 50. Chamber 50 can be a vacuum or lowpressure chamber for use in UV, deep UV, or VUV lithography. Chamber 50can contain any of numerous types atmospheres, such as, nitrogen, etc.Alternatively, lithographic system 10 can be utilized in various othertypes of lithography including lithography that uses radiation at anynumber of wavelengths.

Lithographic system 10 includes a light source 22, a condenser lensassembly 24, a reticle or a mask 18, and an objective lens assembly 26.System 10 can include a stage that supports substrate 12 and can movesubstrate 12 with respect to lens assembly 26. System 10 can have avariety of configurations and arrangements. The configuration of system10 shown in FIG. 1 is exemplary.

System 10 can include mirrors, beam splitters, and other componentsarranged according to other designs. System 10 can be embodied as alithographic camera or stepper unit. An example of lithographic system10 is a PAS5500/1250 series machine manufactured by ASML. Other examplesinclude Microscan DUV systems by Silicon Valley Group or an XLS familyMicrolithography System by Integrated Solutions, Inc. of Korea. Mostpreferably, system 10 is a tool that has varying numerical aperture (NA)such as 11250 (0.85) and V400 (0.93) manufactured by ASML.

Substrate 12 can include one or more layers of material thereon. Thelayers can be insulative layers, conductive layers, barrier layers, orother layers of material which are to be etched, or selectively removedusing the process described herein.

In one embodiment, the layers above substrate 12 are a dielectric layerand a gate conductor layer used to form a gate stack. The dielectriclayer can be a gate oxide and the gate conductor layer can bepolysilicon or metal. The gate stack is configured using the processdescribed below. Various integrated circuit features may be fabricatedusing the method described below.

Substrate 12 and subsequent layers of material are not described in alimiting fashion. The principles of the present invention can be appliedto any integrated circuit substrate, wafer, mask layer, or other layer.Substrate 12 can be conductive, semiconductive, or insulative.

A layer of lithographic material, such as, a photoresist layer ormaterial 16 is deposited or applied over a multilayer anti-reflectivecoating structure 14. In one embodiment, multilayer anti-reflectivecoating structure 14 can be dual layer structure including ananti-reflective coating layer 19 and anti-reflective coating layer 21.Structure 14 preferably serves as a hard mask for subsequent etching oflayers above substrate 14 as well as a coating for optically enhancingresolution by reducing reflections. Thickness and materials for layers19 and 21 are chosen so structure 14 is thin enough to be etched withouteroding material 16 and yet thick enough to provide critical dimensioncontrol and to withstand the etching of layers underneath structure 14.

Photoresist material 16 can comprise any of a variety of photoresistchemicals suitable for lithographic applications. Material 16 can becomprised of a matrix material or resin, a sensitizer or inhibitor, anda solvent. Photoresist material 16 is preferably a high-contrastphotoresist, but may alternatively be a low-contrast photoresist.

Photoresist material 16 is deposited by, for example, spin-coating overlayer of structure 14. Material 16 can be provided with a thickness ofless than 0.5 microns. Preferably, photoresist material 16 has athickness between 0.1 and 0.5 microns. Further, photoresist material 16may be either a positive photoresist or a negative photoresist and canbe a multilayer resist material.

Preferably, the size of features provided to layers 19 and 21, such asperiphery and core features, give imaging at varying effective NA's. For65 nanometer generations and beyond, extremely low reflectivity can beobtained by utilizing dual layer BARC hard masks, such as layers 19 and21 described below.

With reference to FIGS. 1-10, an exemplary process for forming a gatestack or structure is described below as follows. The processadvantageously provides a hard mask with good critical dimension controland anti-reflective coating characteristics.

With reference to FIG. 2, substrate 12 includes a dielectric layer 52and a gate conductor layer 54. Layers 52 and 54 are aconductive/dielectric stack for the formation of a gate structure.Layers 52 and 54 can have a variety of thicknesses and be manufacturedfrom a variety of materials.

In one embodiment, gate conductor layer 54 is poly 2 layer for a flashdevice. Layer 54 can be a 500-2000 Å thick polysilicon layer and layer52 can be a 200 to 1000 Å thick silicon dioxide or silicon nitridelayer. Layers 52 and 54 form a polysilicon oxide pillar.

In one embodiment, a layer 51 of hard mask (HM) oxide material or otherinsulator can be deposited by furnace deposition or CVD above layer 54.Preferably, layer 51 is approximately 300-700 Å thick of oxide material(e.g., SiO₂). Layer 54 can be deposited by chemical vapor deposition(CVD) above layer 52. Layer 52 can be grown or deposited (CVD) abovesubstrate 12.

An anti-reflective coating layer 19 is provided above layer 54 in a step202 of process 100 (FIG. 10). Anti-reflective coating layer 19 can bedeposited by CVD or diffusion furnace. In one embodiment, layer 19 isdeposited as a 200-1000 Å thick layer of silicon rich nitride (SiRN) orSi₃N₄.

With reference to FIG. 3, an anti-reflective coating layer 21 isdeposited above anti-reflective coating layer 19 in a step 204 ofprocess 100. Layer 21 can be deposited by CVD or deposited by spin-ondeposition. The combination of layers 19 and 21 forms a multilayer orbi-layer ARC that also can be used as a hard mask for selectivelyremoving layers 52 and 54 to form gate stacks. In one embodiment, layer21 is a 250 Å thick layer of silicon oxynitride (SiON). Alternativematerials and thickness for layers 19 and 21 may be available.

According to other embodiments, layers 19 and 21 (structure 14) can beSiON over SiON, SiON over SiOC, spin-on organic (n=1.8, k=0.35) overSiRN (300-1000 Å), spin-on organic over any of SiON, SiOC or Si₃N₄. Thespin-on organic can have a k value ranging from k=0.3-0.55. Si₃N₄preferably has a k value greater than the conventional value of 0.22(e.g., has a value of 0.25-0.35). In one preferred embodiment, layer 19is SiRN or SiON and layer 21 is spin-on organic anti-reflective materialwith n=1.8 and k=0.3-0.55.

The thickness of layers 19 and 21 are chosen in accordance with opticalparameters associated with system 10. Preferably, the thickness oflayers 19 and 21 are chosen so that the combination of layers 19 and 21has an anti-reflective effect and yet have a thickness requirementsuitable for use as a hard mask. In a preferred embodiment, thethickness is chosen to be thick enough to avoid erosion when layer 54 isetched and yet thin enough so that photoresist material is not erodedwhen layers 19 and 21 are etched.

System parameters and design considerations can affect the selection ofdimensions and materials for layers 19 and 21. For example, thewavelength of radiation used by system 10 (FIG. 1) can affect theselection of materials and thicknesses for layers 19 and 21. In oneembodiment, system 10 uses radiation having a wavelength of 248 nm,layer 19 is a 400 Å thick layer of organic CVD ARC and layer 21 is a 200Å thick layer of Si rich nitride. Layers 19 and 21 can be the samematerial as each other or different materials from each other.

Applicants have found that according to one embodiment, simulations showthat the thinnest dual BARC layer (layers 19 and 21) with optimalconditions is 250 Å top SiON and 300 Å bottom SiRN. The dual BARC layeris provided above a 450 Å layer (300-700 Å thick) of oxide HM (layer 51which is provided over a 500 Å layer of polysilicon (layer 54)).Applicants have found that the oxide thickness associated with layer 52does not appear to affect the process. The polysilicon layer (layer 54)is preferably a poly 2 layer for a flash gate stack.

In one particular embodiment, layer 54 is a polysilicon layer (500-1500Å and preferably has a 600 Å thickness. Layer 19 is a 400 Å thick SiRN(N=2.664, K=0.25), and layer 21 is a 300 Å thick layer of SiON (N=1.8,K=0.35). Preferably, reflectivities are achievable well below 1%(0.0005-0.0803%).

Examples of other particular embodiments are shown in Table 1 below. Thecoefficients of refraction are represented by n and k where n+ikrepresents the complex index of refraction. Lithography is performed ata wavelength of 193 nm. The underlying layer in Table I is the layerbelow layer 19.

TABLE 1 Layer 19 Layer 21 Underlying Example Material k n ThicknessMaterial n k Thickness Layers 1 SiRN 0.35 2.6 400 Å SiON 1.8 0.35 300 ÅPoly 2 SiRN 0.35 2.6 400 Å SiOC 1.8 0.35 300 Å Poly (N free) 3 Si₃N₄0.25 2.6 400 Å SiON 1.8 0.35 300 Å Poly to 0.35 4 Si₃N₄ 0.25 2.6 400 ÅSiOC 1.8 0.35 300 Å Poly to (N free) 0.35 5 SiRN 1.05 2.2 400 Å SiON 1.80.35 300 Å HM Poly 100-1000 Å 6 SiRN 1.05 2.2 400 Å SiOC 1.8 0.35 300 ÅHM Poly (N free) 100-1000 Å 7 SiRN 1.05 2.2 400 Å Organic 1.8 0.30 300 ÅHM spin-on to AR40 0.55 8 SiRN 1.05 2.2 400 Å SiON 1.8 0.5  300 Å Poly 9SiRN 1.05 2.2 400 Å SiOC 1.8 0.5  300 Å Poly (N free) 10 SiRN 1.05 2.2400 Å Organic 1.8 0.30 300 Å Poly spin-on to AR40 0.55

With reference to FIG. 4, a layer of photoresist material 16 is appliedabove multilayer structure 14 in a step 206 of process 100. Material 16can be applied by spin coating to a thickness of 100-5000 Å. Material 16can be a 2000 Å ArF resist.

With reference to FIG. 5, photoresist material 16 is configured to havea feature 56 according to a conventional lithographic process in asystem, such as, system 10. The lithographic process advantageouslyutilizes the anti-reflective characteristics of structure 14 in a step208 of process 19.

In one embodiment reticle 18 (FIG. 1) is utilized to pattern feature 56in material 16. After exposure to radiation in system 10, material 16 isdeveloped to leave feature 56. In one embodiment, the pattern can be forprinting lines, feature 56 representing the line width of one line.

With reference to FIG. 6, material 16 is subjected to a trim etchingprocess to reduce its dimension in a step 210 of process 100. After thetrim etching process, material 16 includes a feature 62. Feature 62 hasa width less than the width of feature 56 (FIG. 5). The trim etchingprocess is described as an optional step and is not necessary to achievethe advantages of the present invention.

With reference to FIG. 7, layer 21 is removed in accordance with feature16 in a step 212 of process 100. Preferably, a dielectric etchingprocess is utilized to remove layer 21. The etching process can beselective to material 21 with respect to material 16. If materialsassociated with layers 19 and 21 have different etch selectivity,material 16 can be removed after layer 21 is etched. Alternatively, iflayers 19 and 21 have similar etch selectivity, material 16 is notremoved until after layer 19 is etched.

With reference to FIG. 8, layer 19 is etched in accordance with feature16 in a step 214 of process 100. Layer 19 can be etched in a processsimilar to the process used to etch layer 21. In one embodiment, layers19 and 21 can be simultaneously etched. Preferably, layer 19 is etchedin a process selective to the material of layer 19 with respect to gateconductor layer 54.

With reference to FIG. 9, material 16 (FIG. 8) is removed and gateconductor layer 54 and dielectric layer 52 are etched. Alternatively,photoresist layer 16 can remain during the etching of layers 54 and 52.

Gate conductor layer 54 can be etched in a dry etching process selectiveto layer 54 with respect to layer 19 and layer 21. After layer 54 isetched, layer 52 can be etched in a dry etching process selective tolayer 52 with respect to layers 21 and 19.

Material 16 can be removed in an ashing process in a step 216 process100. For example, a conventional ashing process utilizing an O₂ plasmacan remove material 16. Alternatively, other removal processes such aswet strip can strip material 16. Gate conductor layer 54 and dielectriclayer 52 are etched utilizing structure 14 as a hard mask.

Various design criteria can be utilized for layers 19 and 21. Forexample, a designer can chose the required total thickness of structure14 to appropriately etch layers 54 and 52. Knowing the opticalcharacteristics of materials for layers 19 and 21, the thickness oflayers 19 and 21 can be chosen to achieve the desired opticalcharacteristics.

According to one preferred embodiment, a spacer layer is provided abovelayers 19 and 21 after etching and after material 16 is removed. Thespacer layer is etched to leave spacer material in the holes of thepattern. The spacer layer is utilized to reduce the size of holesassociated with the pattern in layers 19 and 21. The spacer layer can beprovided before or after material 16 and layer 21 is removed. Theremaining portions of layers 19 and 21 and the spacer layer are used asa mask to etch layer 54.

Various materials can be used for the spacer layer. The spacer layer canbe made from materials similar to layers 19 and 21 (e.g., SiON, SiRN,oxide, etc.). The thickness of the spacer layer is chosen in accordancewith spacer geometries.

With reference to FIG. 10, flow diagram 200 describes a process forforming a hard mask utilizing structure 14 (FIG. 1). At a step 202, afirst anti-reflective coating (ARC) layer, such as layer 19 is depositedabove a substrate. At a step 204, a second ARC layer is deposited abovethe first ARC layer. The second ARC layer can be a layer such as layer21 (FIG. 3). As discussed above, the materials and thickness of thefirst and second ARC layers are chosen to have superior opticalproperties and yet operate as a hard mask.

At a step 206, a photoresist layer is applied over the second ARC layer.The photoresist layer can be photoresist material 16 (FIG. 1). At a step208, the photoresist layer is patterned in a lithographic system such assystem 10. At a step 210, the photoresist layer is trim etched to form afeature such as feature 62 (FIG. 8) having a smaller critical dimension.At a step 212, the first ARC layer is etched. At a step 214, the secondARC layer is etched. At a step 216, the photoresist layer is removed.The first and second ARC layers can be utilized as the hard mask forforming integrated circuit structures such as gate stacks.

Preferably, layer 19 is removed during etch and layer 21 (bottom SiRNlayer) is a hard mask layer for spacer processes in a dual polyflow. Inaddition, layer 51 can serve as a hard mask for the spacer process fordual polyflow. As described above, the spacer process allows a patternto be formed with smaller holes.

FIGS. 11-49 show graphs detailing characteristics associated with layers19, 21, 51, 52 and 54 using lithography at a wavelength of 193 nm. Inthe FIGS. 11-49, layer #2 refers to layer 21, layer #3 refers to layer19, layer #1 refers to photoresist material 16, layer #4 refers to oxidelayer 51, and layer #5 refers to layer #54. The underlying oxide layerrefers to the insulative layer below layer 54 (layer 52). Thecharacteristics shown in FIGS. 11-49 are not provided in a limitingfashion unless those characteristics are specifically and literallyrecited in the claims.

FIG. 11 shows reflectivity at a numerical aperture set to 0.85. Layer 21is 300 Å low K SiON (n=1.8, k=0.35). Layer 19 is low K SiRN 400 Å thicklayer (n=2.6). Alternatively, layer 19 can be a nitrogen free layer suchas SiOC. Reflectivities of below 0.4% are achieved when layers 19 and 21have an index of refraction of k=0.35.

With reference to FIG. 12, layer 21 is a 300 Å SiON layer and layer 19is a 400 Å SiRN layer. FIG. 12 shows reflectivity over numericalaperture (NA) range from 0.5 to 1.0 and a refractive index for layer 21ranging from k 0.25 to 0.75. Layer 21 has n=1.8 and k varies from0.25-0.75. Layer 19 has a k=0.35 and n=2.664. In FIG. 12, thereflectivity is less than 0.4 percent for all numerical apertures from0.5 to 1.0 if k=0.35 for layer 21.

With reference to FIG. 13, the substrate reflectivity is relativelysmall across a numerical aperture of 0.5 to 1.0. FIG. 13 utilizes alayer 21 that is 300 Å thick and SiON (k=0.25) and a layer 19 that is400 Å thick and SiRN (k=0.35). In FIG. 13, reflectivity is below 0.32percent.

With reference to FIG. 14, the substrate reflectivity is relativelysmall across a numerical aperture of 0.5 to 1.0. FIG. 14 utilizes alayer 21 that is 300 Å thick and SiON (k=0.35) and a layer 19 that is400 Å thick and SiRN (k=0.35). In FIG. 14, reflectivity is below 0.18percent and a minimum at NA=0.85.

With reference to FIG. 15, the substrate reflectivity is relativelysmall across a numerical aperture of 0.5 to 1.0. FIG. 15 utilizes alayer 21 that is 300 Å thick and SiON (k=0.45) and a layer 19 that is400 Å thick and SiRN (k=0.35). In FIG. 15, reflectivity is below 0.23percent.

With reference to FIG. 16, the substrate reflectivity is relativelysmall across a numerical aperture of 0.5 to 1.0. FIG. 16 utilizes alayer 21 that is 300 Å thick (k=0.55) and SiON and a layer 19 that is400 Å thick and SiRN (k=0.35). In FIG. 16, reflectivity is below 0.33percent.

FIGS. 13-16 show that reflectivity is optimized with the k value forlayer 21 set to 0.35.

With reference to FIG. 17, the substrate reflectivity is relativelysmall across a numerical aperture of 0.5 to 1.0. FIG. 17 utilizes alayer 21 that is 300 Å thick and SiON (k=0.35) and a layer 19 that is400 Å thick and SiRN (k=0.25). In FIG. 17, reflectivity is below 0.45percent.

With reference to FIG. 18, the substrate reflectivity is relativelysmall across a numerical aperture of 0.5 to 1.0. FIG. 18 utilizes alayer 21 that is 300 Å thick (k=0.35) and SiON and a layer 19 that is400 Å thick and SiRN (k=0.35). In FIG. 18, reflectivity is below 0.18percent.

With reference to FIG. 19, the substrate reflectivity is relativelysmall across a numerical aperture of 0.5 to 1.0. FIG. 19 utilizes alayer 21 that is 300 Å thick and SiON (k=0.35) and a layer 19 that is400 Å thick and SiRN (k=0.45). In FIG. 19, reflectivity is below 0.23percent.

With reference to FIG. 20, the substrate reflectivity is relativelysmall across a numerical aperture of 0.5 to 1.0. FIG. 20 utilizes alayer 21 that is 300 Å thick and SiON (k=0.35) and a layer 19 that is400 Å thick and SiRN (k=0.55). In FIG. 20, reflectivity is below 0.33percent.

FIGS. 17-20 show that at NA=0.85, layer 16 can be set to a k value of0.35 to achieve reflectivities of 0 to 0.35% (for f=0.25).

With reference to FIG. 21, the substrate reflectivity is relativelysmall across a numerical aperture of 0.5 to 1.0. FIG. 21 utilizes alayer 21 that is 300 Å thick and SiON (n=1.8, k=0.35) and a layer 19that is 400 Åthick and SiRN (n=2.664, k=0.35). Layer 19 is above a 100 Åsilicondioxide layer (e.g. layer 51) over polysilicon (e.g. layer 54).In FIG. 21, reflectivity is below 0.33 percent.

With reference to FIG. 22, substrate reflectivity is relatively smallacross a numerical aperture of 0.5-1.0. FIG. 22 utilizes a layer 21 thatis 300 Å thick and SiON (n=1.8, k=0.35) and a layer 19 that is 400 Åthick and SiRN (n=2.664, k=0.35). Layer 19 is above a 200 Å thicksilicon dioxide layer over polysilicon (e.g., layer 51 over layer 54).FIGS. 21 and 22 show higher reflectivity with the increase in thicknessof the silicon dioxide layer (e.g., layer 51).

With reference to FIG. 23, layer 21 has an n=1.8, k=0.35 and is 300 Åthick of SiON. Layer 19 has the thickness of 350 Å and is SiRN (n=2.664,k=0.8) Layer 51 is from 0 to 60 nanometers thick. Applicants note thathigh K SiRN films with n=2.65 given here are generally not presentlyavailable at 193 nanometers wavelengths. Thicknesses of 100-200 Å forlayer 51 result in a 0.2 percent reflectivity.

With reference to FIG. 24, layer 21 is a 300 Å thick SiON layer havingn=1.8 and k=0.35. Layer 19 is a high K SiRN layer having n=2.2, k=1.05,and a thickness of 400 Å. Layer 51 has a thickness from 0 to 60nanometers and the numerical aperture extends from 0.5 to 1.0. FIG. 24shows reflectivity is extremely low through numerical apertures forthicknesses of layer 51 from 100 Å to 200 Å and even low at thicknessesof 450 Å.

With reference to FIG. 25, layer 21 is a low K SiON layer having n=1.8,k=0.35, and a thickness of 300 Å. Layer 19 is a high K SiRN layer havingN=2.2, K=1.05, and a thickness of 300 Å. The thickness of layer 51 isfrom 0 to 60 nanometers and the numerical aperture extends from 0.5 to1.0. FIG. 25 shows reflectivities are extremely low at thicknesses of450 Å and are low at thicknesses of 100-200 Å for layer 51.

With reference to FIG. 26, substrate reflectivity versus the thicknessof layer 51 is shown. Layer 21 is a low K SiON layer having n=1.8,k=0.35 and a thickness of 300 Å. Layer 19 is a high K SiRN layer havingn=2.2, k=1.05, and a thickness of 300 Å. Layer 51 has a thickness from 0to 60 nanometers and NA=0.85. FIG. 16 shows a reflectivity of below0.23% for all values of thickness for layer 51.

With reference to FIG. 27, substrate reflectivity versus the thicknessof layer 51 is shown. Layer 19 and 21 are a dual SiON type in whichlayer 21 is an SiON material, having a thickness of 300 Å (n=1.8,k=0.35). Layer 19 is an SiON layer having a thickness of 350 Å (n=1.9,k=0.65). FIG. 27 shows that the reflectivity is 0.2% or less for 100 Åor less thickness of layer 51. Reflectivity is a minimum between 50 and100 Å.

With reference to FIG. 28, reflectivity is shown with respect tonumerical apertures and thicknesses for layer 51. Layer 19 is a 400 ÅSiON layer (n=1.9, k=0.65). Layer 21 is a 300 Å SiON layer (n=1.8,k=0.35). FIG. 28 shows lower reflectivity for lower HM oxide thicknessesfor layer 51. In addition, FIG. 28 appears to show that reflectivitiesare better with a low K SiON/high K SiRN coating rather than a dual SiONcoating in certain circumstances.

With reference to FIG. 29, reflectivity is shown with respect to thethickness of layers 19 and 21. Layer 19 is SiRN as n=2.2 and k=1.05.Layer 21 is an SiON layer having n=1.8 and k=0.35.

With reference to FIG. 30, reflectivity is shown with respect tothicknesses of layers 19 and 21 where a structure is similar to thatdiscussed with respect to FIG. 29. However, layer 21 has an index ofrefraction with k=0.5.

With reference to FIG. 31, reflectivity is shown with respect tothicknesses of layers 19 and 21 where a structure is similar to thestructure of FIG. 29. However, layer 219 is provided above a 1000 Åsilicon dioxide layer which is above a 1000 Å polysilicon layer (e.g.,layer 51 over layer 54).

With reference to FIG. 32, reflectivity is shown with respect tothicknesses of layers 19 and 21. The structure utilized in FIG. 32 issimilar to the structure of FIG. 31; however, layer 19 has a k valueequal to 0.50.

With reference to FIG. 33, substrate reflectivity versus numericalaperture is shown. Layers 19 and 21 are dual bottom anti-reflectivecoatings (BARCs). Layer 21 is spun on as a 300 Å BARC layer above a 350Å bottom BARC layer above a 1000 Å polysilicon layer.

With reference to FIG. 34, reflectivity is shown with respect tonumerical aperture for a structure similar to the structure of FIG. 33;however, layer 19 is provided above a 1000 Å SiON layer which is above a1000 Å polysilicon layer.

With reference to FIG. 35, reflectivity is shown with respect tonumerical apertures for a structure similar to the structure of FIG. 33;however, layers 19 and 21 are inorganic BARC layers.

With reference to FIG. 36, reflectivity is shown with respect tonumerical apertures. FIG. 36 utilizes structures similar to FIG. 35;however, layers 19 and 21 are provided above a 1000 Å SiON layer whichis above a 1000 Å polysilicon layer.

With reference to FIG. 37, layer 21 is a low K SiON layer (n=1.8,k=0.35, and thickness=300 Å and layer 21 is a high K SiRN layer (n=2.2,k=1.05, thickness=400 Å). The numerical aperture is adjusted from 0.5 to1.0 and the thickness of layer 51 ranges from 0 to 600 nanometers. FIG.37 shows that the reflectivity is extremely low across numericalapertures when layer has a thickness of 100-200 Å. Reflectivity is lowat thicknesses of 450 Å.

With reference to FIG. 38, layers 19 and 21 are a dual BARC combination.Layer 21 is a low K SiON layer (n=1.8, k=0.35, thickness=300 Å and layer19 is a high K SiRN layer (n=2.2, k=1.05, and thickness=300 Å). Thenumerical aperture is adjusted from 0.5 to 1.0 and the thickness oflayer 51 is between 0 and 600 Å. FIG. 37 shows reflectivity is extremelylow at thicknesses of 450 Å for numerical apertures is 0.5 to 1.0 andremains low at thicknesses of 100-200 Å.

With reference to FIG. 39, structure 14 includes a 300 Å SiON layer 21and a 400 Å SiRN layer 19. Reflectivity is as shown across the spectrumof thicknesses for layer 51 and layer 52. Thickness of layer 52 rangesfrom 0 to 150 nanometers and thickness for layer 51 ranges from 30-90nanometers. Numerical aperture is fixed at 0.85. FIG. 39 shows contoursfor reflectivity are flat about a 500 Å minimum thickness for layer 52.Thickness of layer 52 can range between 500 and 1500 Å below layer 51,which is oxide HM. Oxide depth beneath a minimum thickness of 500 Å ofpolysilicon does not change reflectivity

With reference to FIG. 40, reflectivity with respect to the thicknessesof layers 21 and 19 is shown. Layer 51 is a 450 Å oxide HM layer andlayer 52 is a 500 Å poly silicon layer above a 600 Å oxide layer. Withreference to FIG. 40, reflectivity is shown with respect to thethickness of layers 19 and 21. Layers 19 and 21 are above a 450 Å oxideHM layer 51 above a 500 Å poly silicon layer 54 above a 600 Å oxidelayer.

Layer 21 is a thickness of 16 nanometers to 34 nanometers and layer 19has a thickness from 20 nanometers to 40 nanometers. Reflectivities arelowest or thickness of a 250 Å layer 21 and a 300 Å layer 19. Thenumerical aperture is 0.85.

With reference to FIG. 41, substrate reflectivity is shown with respectto the thickness of a silicon dioxide layer underneath layer 52. Layer21 is a 250 Å SiON layer and layer 19 is a 300 Å SiRN layer. Layer 51 isa 450 Å SiO₂ layer with a 500 Å polysilicon layer 52. The layerunderneath layer 52 is varied from 300 Å to 1000 Å. The effect ofthickness of the layer underneath layer 52 is very close to zero.

FIG. 42 shows substrate reflectivity with respect to the thickness oflayer 51. Layer 21 is an SiON 250 Å thick layer, and layer 19 is a 300Åthick SiRN layer. Layer 54 is a 500 Å thick poly layer above a 600 Åoxide layer. The thickness of layer 51 is varied from 300-800 Å.Reflectivity is a minimum of 0.15% at 450 Å.

With reference to FIG. 43, substrate reflectivity is shown with respectto the thickness of layer 51. Layer 21 is a 200 Å thick SiON layer andlayer 19 is a 300 Å thick SiRN layer. Layer 54 is a 500 Å poly layerabove a 600 Å oxide layer 52. Layer 51 has a thickness from 30 nm to 80nm. A minimum reflectivity is shown at approximately 450-500 Å for layer51.

With reference to FIG. 44, substrate reflectivity is shown with respectto the thickness of layer 51. Layer 19 is a 300 Å thick SiON layer andlayer 21 is a 300 Å thick SiRN layer. Layer 54 is a 500 Å poly layerabove a 600 Å oxide layer. Layer 51 is a HM oxide layer. FIG. 44 shows aminimum reflectivity at approximately 450 Å. In FIGS. 41-44,reflectivity varies between 0.1% and 0.8% for HM thickness at 450 Å withlayer 21 in a range of 250 Å plus/minus 50 Å and layer 19 fixed at 300Å.

With reference to FIG. 45, substrate reflectivity is shown with respectto the thickness of layer 21. Layer 51 is a 450 Å thick oxide layer, andlayer 54 is a 500 Å thick polysilicon layer above a 600 Å oxide layer.Layer 19 is a 300 Å SiRN BARC layer. The thickness of layer 21 is variedfrom 15 nm to 35 nm. FIG. 45 shows that a minimum is reached atapproximately 250-300 Å thick layer for layer 21. The applicants havefound optimal simulations as follows: 250 Å SiON for layer 21, 300 ÅSiRN for layer 19, 500 Å of polysilicon for layer 54, and 450 Å foroxide HM for layer 51.

FIG. 46 shows reflectivity for a spin-on dual BARC structure 14 oversilicon dioxide HM over polysilicon. Layer 21 is an organic spin-on BARClayer (n=1.8, k=0.5), and layer 19 is an SiRN layer (n=2.2, k=1.05).Minimum reflectivities are shown for thicknesses of layer 21 between 300and 400 Å and layer 19 for thicknesses of 250-300 Å.

FIG. 47 shows substrate reflectivity versus a thickness of layer 21 fororganic spin on BARC. Layer 21 is a spin-on Organic BARC layer. Layer 19is a 250 Å SiRN layer above a 200 Å SiO₂ layer 51. Minimum reflectivityis associated with a thickness of 350 Å.

With reference to FIG. 48, substrate reflectivity is shown with respectto the thickness of layer 21. A 300 Å thick SiO₂ layer 51 is below a 250Å thick SiRN layer 19. Layer 21 is preferably spun on (n=1.8, k=0.5). Areflectivity minimum is shown between 300 and 350 Å for layer 21.

With reference to FIG. 49, reflectivity is shown with respect to thethickness of layer 21. Layer 51 is 400 Å SiO2 layer. Layer 19 is a 250ÅSiRN layer. Layer 21 is preferably spun on (n=1.8, k=0.5). FIG. 49shows a minimum reflectivity at approximately 300 Å.

It is understood that while the detailed drawings, specific examples,material types, thicknesses, dimensions, and particular values givenprovide a preferred exemplary embodiment of the present invention, thepreferred exemplary embodiment is for the purpose of illustration only.The method and apparatus of the invention is not limited to the precisedetails and conditions disclosed. For example, although specific typesof ARC materials and thicknesses processes are mentioned, othermaterials and process steps can be utilized. Various changes may be madeto the details disclosed without departing from the spirit of theinvention which is defined by the following claims.

1. A method of forming a gate stack for an integrated circuit, the method comprising: forming an oxide layer above a gate conductor layer and a substrate; forming a first anti-reflective coating layer and a second anti-reflective coating layer above the oxide layer; forming a photoresist layer over the second anti-reflective coating layer; patterning the photoresist layer to form a first feature in the photoresist layer at a high numerical aperture; selectively removing the first and second anti-reflective layers in accordance with the first feature; forming a spacer layer; etching the spacer layer; and etching the oxide layer and the gate conductor layer to form the gate stack.
 2. The method of claim 1, wherein the second anti-reflective coating layer has a thickness of approximately 250 Å.
 3. The method of claim 2, wherein the first anti-reflective coating layer has a thickness of approximately 300 Å.
 4. The method of claim 3, wherein the first anti-reflective coating layer includes silicon oxynitride.
 5. The method of claim 4, further comprising forming the gate conductor layer above the substrate, the first anti-reflective coating layer being formed above the gate conductor layer.
 6. The method of claim 4, wherein the photoresist layer is high contrast ARF, KRF, or I-line resist.
 7. The method of claim 1, further comprising: forming the spacer layer after selectively removing the first and second anti-reflective coating layers; and etching the spacer layer before etching the gate conductor layer.
 8. The method of claim 1, further comprising: etching the gate conductor layer above the substrate in accordance with the first anti-reflective coating layer, the second anti-reflective coating layer, and the spacer layer.
 9. The method of claim 1, wherein the first anti-reflective coating layer includes at least one of Si₃N₄, SiOC, SiRN, and SiON, wherein the second anti-reflective coating layer includes at least one of organic spin on antireflective material, SiOC, SiRN and SiON.
 10. The method of claim 1, wherein the first anti-reflective coating layer is applied to the oxide layer and includes silicon rich nitride. 